Abstract

By using a pump-probe technique, we have observed the nascent rotational population distribution of in the with a reaction, which is endothermic by 1680 cm−1. The distribution yields a single rotational temperature at ∼770 K, but the population in the level is not detectable. According to the potential energy surface (PES) calculations, the insertion mechanism in (near) collision geometry is favored. The collision is initially along the surface in the entrance channel and then diabatically couples to the ground surface, from which the products are formed. From the temperature dependence measurement, the activation energy is evaluated to be indicating that the energy required for the occurrence of the reaction is approximately the endothermicity. As Li is excited to higher states or we cannot detect any LiH product. From a theoretical point of view, the surface, correlating with the Li state, may feasibly couple to a repulsive surface, from which the collision complex will rapidly break apart into and The probability for further surface hopping to the or surfaces is negligible, since the and surfaces are too far separated to allow for an efficient coupling. The state is expected to behave similarly. The observation also provides indirect evidence that the harpoon mechanism is not applicable to this system.